The present invention relates generally to an internal combustion engine having an exhaust driven turbocharger and more particularly to control a wastegate in response to pressure in an exhaust system.
Due to desired performance characteristics of internal combustion engines, exhaust gas driven turbochargers must be regulated to achieve desired charge-air pressures over a wide range of engine speeds. Charge air pressure is related to turbocharger speed and turbocharger speed is related to the flow of an exhaust gas stream through a turbine portion of the turbocharger. Many exhaust driven turbochargers include a wastegate that permits a portion of the exhaust gas stream of the engine to bypass the turbine portion.
Typical exhaust driven turbochargers have a pressure responsive canister control module that is operably connected to the wastegate. The canister control module includes a movable diaphragm (or piston) having a linkage and a spring or biasing member. The piston is exposed to atmospheric pressure and the spring on one side and a charge air pressure on the other side. As the charge air pressure increases beyond a predetermined value, the piston and linkage are moved toward the biasing member, causing the wastegate to open, in turn slowing the turbocharger.
However, some internal combustion engines, such as those used in some large work machines, are configured to operate in a manner that may prevent this type of control strategy from working well. One such example is, an internal combustion engine configured to have a high torque rise in relation to engine speed. In other words, the engine is configured so that as the engine speed is decreased, the output torque of the engine is increased at a faster than normal rate. To help increase the torque at a faster rate, the turbocharger is configured to provide higher charge air pressure at lower engine speed.
One disadvantage with this type of engine configuration is that the charge air pressure does not vary much over the normal operating range of engine speed. Due to the lack of charge air pressure variation, wastegate control strategies based on charge air pressure may not provide enough control of the turbocharger. This may cause the turbocharger to operate at extremely high speeds, resulting in damage or reduced turbocharger life.
One example of a control system that does not use charge air to control the wastegate is U.S. Pat. No. 5,205,125 issued to General Motors Corporation on Apr. 27, 1993. In this system the wastegate is controlled by the pressure of the exhaust pushing the wastegate open. Additionally, the wastegate assembly includes an adjustable biasing mechanism to control how much pressure is required to open the wastegate.
One possible problem related to using exhaust pressure to control the wastegate is that exhaust pressure fluctuates greatly as each exhaust valve opens. Also, the temperature of exhaust gas is much higher than that of charge air exiting the compressor portion. Existing canister control modules may not operate with the extreme temperatures of exhaust gas. Particulates in the exhaust gas may build up in a control mechanism and reduce dependability of the control system.
This invention is directed to overcoming one or more of the above identified problems.
In an aspect of the present invention, a mechanism is provided for controlling the wastegate of a turbocharger. The mechanism includes a canister control module, a conduit having a first end in fluid communication with an exhaust system and a second end in fluid communication with the canister control module. An actuator is positioned in the canister control module and is responsive to pressure from the exhaust system. The actuator being adapted to move the wastegate between a first and a second position, the first position allowing fluid communication between the exhaust system and a turbine portion of the turbocharger and the second position allowing partial bypassing of the turbine portion.
In another aspect of the present invention, a method for controlling a wastegate of a turbocharger is provided. The method includes directing a portion of exhaust gas from an exhaust system to an actuator, exerting a force with the portion of exhaust on the actuator and moving the wastegate to the open position when exhaust gas is above a predetermined pressure.
In yet another aspect of the present invention, is an internal combustion engine having a control mechanism for controlling the wastegate of a turbocharger. The control mechanism includes a canister control module having a pressure region, a conduit in fluid communication with the canister control module and an exhaust system, and an actuator positioned in said canister control module. The actuator is adapted to move the wastegate between a first and a second position, in the first position the wastegate allows fluid communication between an exhaust system and an inlet to a turbine in the turbocharger. In the second position the wastegate permits partial bypassing of the turbine portion.